Factors influencing barley germination and malt quality.

Abstract

Methods for the determination of total bromine, free bromate and gibberellic acid in germinating grain have been developed. Using these methods the effectiveness of bromate and gibberellic acid in controlling the modification of barley in malting has been assessed in terms of the uptake and utilisation of these compounds in germinating grain and then more practically in terms of their combined effects on the development of beta-glucanase activity in germination. Bromate applied to steeped barley enters the grain rapidly within four hours of application, it is reduced to bromide as germination proceeds but survives in the endosperm until kilning. Bromate has not been detected in kilned malt. Results obtained with selected, undamaged grains of both Proctor barley and Nackta (Naked) barley suggest that bromate has the property of penetrating the sound testa of a barley corn and gaining rapid access to the endosperm. This property is the main reason for the profound effectiveness of bromate in controlling germination and shows that the barley testa membrane does not show perfect semi-permeability. Compounds (potassium iodate, azodicarbonamide) which have similar effects to bromate in dough fermentation do not act similarly in malting. Iodate is much more rapidly reduced than bromate at the testa and so less free iodate enters the endosperm and it is thus not as effectively utilised by the germinating grain. The barley endosperm bioassay for gibberellic acid is affected by barley age and variety and these observations may have practical applications. After 24h germination the level of endogenous gibberellin-like material present in the grain is approximately 1.4 ng/corn. The biological activity of the total gibberellin-like material extracted from grain treated with gibberellic acid falls during germination although significant quantities of applied gibberellic acid have entered the grain during the first 24h of germination. Application rates in excess of 0.1 mg/kg are probably necessary to effectively supplement the natural gibberellin level. The development of beta-glucanase activity in germination can be increased by combined or single treatments of gibberellic acid and bromate. This is particularly valuable with poorer malting barley varieties like Julia. This is a further useful property of bromate which is not shared by iodate and other compounds used in baking. beta-Glucanase activity of malt is an important factor in mash tun performance when high levels of solid adjunct such as flaked barley are being used. Methods for the determination of beta-glucan throughout the malting and brewing processes have been investigated. The yield and viscosity of beta-glucan extracted from barley is dependent on the length and temperature of extraction. Extremely high viscosity material is extracted at 95°C. In malting high viscosity beta-glucan is released after two days germination but this is broken down in the later stages and the beta-glucan content of finished malt is less than 0.1% of the dry weight. Ethanol precipitation is the most useful technique for practical determinations of beta-glucan in beer. The so-called selective hydrolysis techniques may have insufficient precision to yield meaningful results.

Date of Award	1975
Original language	English
Awarding Institution	University of Bath